Conveyor induction system

ABSTRACT

A conveyor induct system includes a control point subsystem for measuring the point at which control of an article transitions from one conveyor to another. The induct system also includes a subsystem for accurately creating or controlling the gaps between articles on the conveyor system. The control point subsystem monitors the location, and changes in the speed, of an article as it passes between two conveyors operating at different speeds. The gap control subsystem provides real time monitoring and measuring of the package gaps. The measured package gaps are fed into a feedback control system which alters the speed of a conveyor in order to change the gapping as desired.

[0001] This application claims priority to commonly assigned, U.S.provisional application Ser. No. 60/203,301, filed May 11, 2000, andentitled Induct for Next Generation Sorter.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to conveyor systems, and inparticular to the induction section of a conveyor sortation system. Theinduction section of a conveyor system generally refers to the portionof the conveying system in which articles are inducted, or initiated,into the conveying sortation system. The induction section typicallyperforms the function of providing the proper gaps between packages, orother articles traveling on the conveying system, so that the packagescan be sorted for proper distribution. The proper gapping betweenarticles on the conveying system is important for a variety of reasons.First, the gapping of the articles affects the throughput of theconveying system, which is often a factor of high commercialsignificance. By reducing the gaps between articles on the conveyingsystem, the number of articles that can be placed on the conveyingsystem at a given time is increased. By being able to place morearticles on the conveying system at a given time, more articles aremoved over a given time period, thus increasing the throughput of theconveying system.

[0003] Second, the gapping of the articles is highly important becausethe gapping affects the sortation functions of the conveying system.Where the conveying system functions to sort the articles beingconveyed, prior art conveying systems have often used pusher shoes orother diverting means to push the articles off of a main conveyor ontoone or more branch conveyors. In order for these pusher shoes to sortthe packages correctly, it is important that sufficient space beprovided between articles so that the pushers do not inadvertently pushagainst another article while they are in the process of diverting asecond article. Further, pusher shoes on some sorters tend to rotate thearticle, at least partially, when they are in the process of divertingthe article onto a branch conveyor. This rotation ensures that thearticles are properly aligned with the branch conveyor when they arediverted. In order for the article to be rotated, however, it isnecessary for there to be a space behind the article in order to provideroom for the rotation of the article. If insufficient space is allotted,the article may contact another article while being rotated, thuscausing it to enter the branch conveyor misaligned, or to not bediverted at all.

[0004] The sortation functions of the conveying system therefore weighin favor of providing a certain amount of gapping between articles whilethe throughput considerations weigh in favor of reducing this gapping toas small a space as possible. In order to best balance these competinginterests, the induct portion of the conveying system would ideally beable to consistently and accurately produce gaps that were just largeenough to accommodate the gapping requirements of the sortation sectionof the conveying system while rarely, if ever, exceeding these minimumgapping requirements. Prior art induct systems, however, have left roomfor improvement as to the consistency, accuracy, and speed at which atwhich gapping of the articles can be performed. Particularly asincreases in throughput have been based on increasing conveyor speedwhile reducing gapping, the necessity for precise gapping in conveyorsystems has increased.

[0005] One reason for the less than desirable performance of priorinduct systems has been the inaccuracies that result in controlling anarticle as it transitions from one conveyor to another. Because gappingbetween articles can only be changed by changing the speed of onearticle with respect to another article, the creation and control ofgaps tends to occur by utilizing at least two conveyors. For example, ifan upstream conveyor is traveling at a first speed and a downstreamconveyor is traveling at a different speed than the first conveyor, anarticle moving from the upstream conveyor to the downstream conveyorwill increase the gap between it and any trailing package behind it asit passes onto the downstream conveyor. This increase in gap is due tothe acceleration of the article as it initially arrives on the secondconveyor. For a certain amount of time, the leading article is travelingat a higher speed (the speed of the downstream conveyor) than thetrailing article, which is traveling at the speed of the upstreamconveyor. This difference in speeds enlarges the gap between the twoarticles.

[0006] In the past, the controlling of gaps by using multiple conveyorstraveling at different speeds has resulted in inaccuracies of thecreated gap partially because the point at which an article switchesfrom having its speed controlled by the upstream conveyor to thedownstream conveyor has not been able to be accurately determined. Whilethis point is often assumed to correspond to the moment when the centerof gravity of the article reaches the midpoint between the upstream andthe downstream conveyors, this assumption often proves incorrect, thusleading to inaccuracies in the created gaps.

[0007] The creation of gaps in prior art conveying systems has also beeninaccurate because these prior art conveying systems are not able toaccurately determine the position of articles on the conveyors. Forexample, in some prior art conveying systems, the position of thearticle was determined by sensing the passing of the article by a singlephoto-detector positioned alongside the conveyor. As the article movedpast the single photo-detector, its position was computed by computinghow far the conveyor belt had moved since the article had been detected.Determining how far the conveyor belt had moved often was carried out byway of an encoder that measured the amount of rotations of the motorthat powered the conveyor belt. Due to measurement inaccuracies,slippage, and other factors, this calculation of the article's positionon the conveyor has a significant uncertainty. This uncertainty of thearticle's position on the conveyor makes controlling the created gaps inprior art induct systems difficult.

[0008] In light of the foregoing disadvantages of the prior art, theneed for an induct system that improves the accuracy and consistency ofthe created gaps between articles can therefore be seen.

SUMMARY OF THE INVENTION

[0009] Accordingly, the present invention provides an improved methodand apparatus for inducting articles into a conveying system. The methodand apparatus allow the position of articles traveling on individualconveyors to be more accurately determined, thus aiding the accuracy andprecision of the gapping process. The method and apparatus of thepresent invention also allow an accurate determination, rather than anassumption, to be made as to the point at which an article moving fromone conveyor to another changes from having its speed controlled by theupstream conveyor to that of the downstream conveyor.

[0010] According to one aspect of the present invention, a method isprovided for determining the control point of an article traveling on aconveyor system. The method includes providing a first and a secondconveyor. The first conveyor includes a downstream end that is alignedwith an upstream end of the second conveyor. The method further includesdetecting when a change occurs in the speed of the article due to thearticle having reached the second conveyor. According to another aspectof the present invention, a method for controlling a gap between a firstand a second article on a conveyor is provided. The method includesproviding a first and a second conveyor which are aligned with eachother. The speed of the second conveyor is set to be different than thespeed of the first conveyor. The control point of the first article ismeasured as the first article passes from the first conveyor to thesecond conveyor. Any gap between the first article and the secondarticle is measured while the first article is traveling at leastpartially on an adjustable speed conveyor. The measured gap is comparedto a desired gap, and the speed of the adjustable speed conveyor isadjusted in order to reduce any difference between said measured gap andsaid desired gap.

[0011] According to still another aspect of the present invention, amethod is provided for creating a gap between a first article and asecond article. The method includes providing a first and a secondconveyor which are aligned with each other. The first conveyor is anadjustable speed conveyor. Any gap between the first and the secondarticle is repetitively measured while the first article is at leastpartially positioned on the first conveyor. Any difference between themeasured gap and a desired gap is calculated. A feedback controller isprovided which takes the difference between the measured gap and thedesired gap and outputs a command for adjusting the speed of theadjustable speed conveyor. The outputted command is based upon thedifference between the measured gap and the desired gap.

[0012] According to still further aspects of the present invention,apparatuses for carrying out the above-described methods are provided.The measuring of the gap between articles may be accomplished by way ofa horizontal array of photo-detectors. The determination of the controlpoint of an article may also be carried out by way of a horizontal arrayof photo-detectors. The determination of the size of a gap, as well asthe issuance of a speed command based upon the size of that gap, mayalso be repeated multiple times for an individual gap. In this manner,direct feedback is provided to the speed controller for the adjustablespeed conveyor as the gap is either maintained or changed. The feedbackcontroller may be a proportional-integral-derivative type controller. Instill further aspects of the present invention, the methods andapparatuses for determining the control point of an article can becombined with, or utilized separately from, the methods and apparatusesfor creating a gap.

[0013] The methods and apparatuses of the present invention provide animproved induction system that allows gaps to be created betweenpackages that are more accurate and consistent, as well as allowing theinduction system to operate at higher speeds while maintaining thisimproved accuracy and consistency. These and other advantages of thepresent invention will be apparent to one skilled in the art in light ofthe following specification when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a combination plan view and block diagram of a conveyorsystem and controller according to one aspect of the present invention;

[0015]FIG. 2 is a plan view of a conveyor system according to anotheraspect of the present invention illustrated at a first moment in time;and

[0016]FIG. 3 is a plan view of the conveyor system of FIG. 2 illustratedat a later moment in time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will now be described with reference to theaccompanying drawings wherein like reference numerals correspond to likeelements in the several drawings. A conveyor induct system 20 isgenerally depicted in plan and block diagram form in FIG. 1. Conveyorinduct system 20 comprises two subsystems which can be utilizedindependently from each other or in combination with each other. Onesuch subsystem is a control point determination module 38 which servesto accurately determine the location of the control points on individualarticles, as will be explained in more detail below. The other subsystemof conveyor induct system 20 is a gap control system 40 which controlsthe speed of one or more of the conveyors in order to create a desiredgap between articles as they exit onto a take-away conveyor 32. By wayof background, such controlling of gaps is also described incommonly-owned U.S. Pat. Nos. 5,267,638 and 5,038,911, the disclosuresof which are hereby incorporated herein by reference. The disclosure ofcommonly-assigned U.S. provisional application Ser. No. 60/203,301,filed May 11, 2000, to which this application claims priority, is alsohereby incorporated herein by reference.

[0018] Conveyor induct system 20 includes a first conveyor 22 and asecond conveyor 24, both of which carry packages or other articles ontheir conveying surfaces 26 in the direction indicated by arrow 28. Theparticular type of conveying surface 26 is not limited within the scopeof the present invention, but can include belts, rollers, slats, and anyother type of conveying structure capable of transporting goods. A feedconveyor, which may include an accumulation conveyor 30, feeds packagesto induct system 20. A take-away conveyor 32 carries packages that havebeen properly gapped to a sortation system (not shown) or otherdownstream junction. Conveyors 30 and 32 are only partially illustratedin FIG. 1. Take away conveyor 32 is located downstream of, and alignedwith, second conveyor 24 and transports articles that are transferredonto it from second conveyor 24. It will be understood that thedimensions of conveyors 22, 24, 30, and 32 are not necessarily drawnaccording to scale, and that the lengths and widths of these conveyorscan vary as would be understood by one skilled in the art. A series ofarticles 34 a-h ride on the conveying surfaces 26 of the variousconveyors and move in the direction of arrow 28. Articles 34, which arenot part of the invention, are depicted in various sizes and are againnot necessarily drawn to scale but are depicted for purposes ofdescription herein.

[0019] As can be seen from articles 34 a, b, and c, the articles 34 thatenter into conveyor induct system 20 from accumulation conveyor 30 maybe generally closely packed together such that no gaps exist betweenthese articles. While it is not necessary within the scope of theinvention that such lack of gaps exists, it is desirable that excessivegaps be removed or minimized prior to the articles reaching firstconveyor 22. Because articles are often manually loaded onto theconveyor system by workers unloading trucks, or other vehicles, there isoften a significant amount of spacing that initially exists betweenarticles as they are first unloaded. This spacing may be on the order ofseveral feet and is desirably eliminated or reduced before the articlesreach first conveyor 22. To that end, it may be desirable to mergeseveral incoming conveyors into a single conveyor line so that gaps canbe reduced or eliminated. While such merging of conveyors may cause areduction in the average gap between packages, there still may existindividual gaps of varying size. An accumulation conveyor helps removethese gaps, provided articles are being fed into the conveyor system ata fast enough rate. It will be understood, however, that an accumulationconveyor is not a necessary component of the present invention. If anaccumulation conveyor is used, it can be any of a variety of types ofconventional accumulation conveyors, or other types of accumulationconveyors, as would be known by one skilled in the art.

[0020] First conveyor 22 preferably, although not necessarily, operatesat a speed that is no greater than the highest speed of the immediatelyupstream conveyor, which, as illustrated in FIG. 1, is accumulationconveyor 30. By limiting the speed of first conveyor 22 to that of themaximum speed of accumulation conveyor 30, articles that travel fromaccumulation conveyor 30 onto first conveyor 22 will not have eithertheir leading or trailing gaps increased. The gapping between articleschanges when the articles transition from first conveyor 22 to secondconveyor 24. First conveyor 22 has a speed which is generally less thanthat of second conveyor 24 so that any gaps between articles will beenlarged as they pass from first conveyor 22 to second conveyor 24.While not required, first conveyor 22 may have its speed set at a fixedratio to that of second conveyor 24 so that changes in the speed ofsecond conveyor 24 will cause proportionate changes in the speed offirst conveyor 22. Alternatively, it may be desirable to control thespeeds of first and second conveyors 22 and 24 so that at certain timesthey operate at the same speed, while at certain other times theyoperate at different speeds.

[0021] An example of a gap created by the passage of articles from firstconveyor 22 to second conveyor 24 can be seen between articles 34 e and34 d. This gap will continue to increase until article 34 d has passedsufficiently onto second conveyor 24 such that article 34 d is carriedat the same speed as second conveyor 24. After article 34 d hastransitioned onto second conveyor 24, the created gap between article 34d and e may or may not be equal to the desired gap. The creation of thedesired gap is accomplished during the transition of articles fromsecond conveyor 24 to take-away conveyor 34. An example of a desired gapis illustrated in FIG. 1 between the trailing edge of article 34 h andthe leading edge of article 34 g.

[0022] In order to more accurately control the gap between articles asthey travel between two conveyors of different speeds, it is helpful toknow precisely when the article will shift from moving at the speed ofthe first conveyor to moving at the speed of the second conveyor. Thisinformation can be gained by using control point determination module 38in order to find the location of the control point of each article. Thecontrol point of an article is the point on the article which, when itis aligned with a specified reference point on the conveyor, willdesignate the moment in time that the article's speed switches frombeing controlled by one belt to another belt. It is important to knowthe control point of an article during the gapping phase of the articlesbecause adjustments in the speed of a conveyor during gapping will beineffective in changing the speed of the article unless the article isstill being controlled by the particular conveyor whose speed is beingadjusted.

[0023] Control point determination module 38 includes a horizontal arrayof photo-detectors 42 which comprise a first array of photo-emitters 44and a second set of photo-receptors 46. The emitters 44 are positionedon an opposite side of first conveyor 22 across from, and aligned with,receptors 46. As would be understood by one skilled in the art, theparticular side on which emitters 44 and receptors 46 is immaterial solong as the emitters are opposite the receptors. Photo-detector array 42emits electromagnetic signals, such as light, infrared, or othersignals, from emitters 44 across first conveyor 22 to receptors 46,which detect the emitted signal provided there is no article on firstconveyor 22 that obstructs the line of sight between an emitter 44 and areceptor 46. Photo-detector array 42 is thus able to determine wheregaps between articles are located by determining which particularphoto-detectors are not obstructed at a given moment. Horizontal arrayof photo-detectors 42, which is often referred to as a light curtain,can be any type of conventional array of photo-detectors, such as thosethat are commercially available from Kore Computing of Comstock Park,Mich., or SICK, Inc. of Bloomington, Minn. Other types ofphoto-detectors can also be used. Photo-detector array 42 should includephoto-detectors that are spaced relatively closely together so thataccurate information can be gathered about the location of gaps and theposition of articles traveling on first conveyor 22. While otherspacings are within the scope of the invention, a photo-detectorpositioned every five millimeters along the length of horizontal array42 is contemplated. More compactly spaced photo-detectors would, ofcourse, give more precise information about the location of articles andgaps, if all other factors remain equal.

[0024] Photo-detector array 42 should give updated information about theentire array of photo-detectors multiple times a second, such as onceevery two milliseconds, although this update rate can vary widely withinthe scope of the present invention, particularly with respect to fasterupdate rates. The height at which photo-detector array 42 is positionedabove conveying surface 26 should be very slight so that photo-detectorarray 42 does not overlook articles traveling on the conveyor that areof very low height. The precise height of array 42 can therefore bevaried depending upon the types of articles being sorted. In general, aheight above conveying surface 26 of a few millimeters should beappropriate for most situations. It may also be desirable to includemultiple arrays of photo-detectors 42 which are vertically stacked uponeach other to give height information about articles, as well asinformation about article shape. The length of photo-detector array 42is preferably, although not necessarily, at least half as long as thegreatest expected article length. Where first conveyor 22 is expected tobe used in an application that transports articles of considerablelength, the length of array 42 should therefore be correspondinglyincreased. Photo-detector array lengths that are less than half of thegreatest expected article length still fall within the scope of theinvention, but do increase the probability of not being able toaccurately determine an article's control point, as the followingdiscussion will illustrate.

[0025] Control point determination module 38 determines the location ofcontrol points on individual articles with respect to a particularreference point. In FIG. 2, a one dimensional frame of reference 48 isillustrated and oriented parallel to first and second conveyors 22 and24. A reference point 50 is designated on frame of reference 48.Reference point 50 is located halfway between the downstream end offirst conveyor 22 and the upstream end of second conveyor 24. A controlpoint 52 is depicted on article 34 d. When control point 52 reachesreference point 50, i.e. it becomes aligned with reference point 50, thecontrol of article 34 d will switch from first conveyor 22 to secondconveyor 24. Thus article 34 d, in the position illustrated in FIG. 2,is being controlled by first conveyor 22 despite the fact that a portionof article 34 d is located on second conveyor 24. The precise momentwhen control switches from first conveyor 22 to second conveyor 24 islargely dependent upon the frictional characteristics of the article andthe conveyor, as well as the center of gravity of the particulararticle. While in the past the control point was often assumed to be thecenter of the article, control point determination module 38 actuallymeasures the location of the control point.

[0026] Control point determination module 38 measures the location of anarticle's control point by monitoring the gap, if there is one, betweenthe trailing edge of article 34 d and the leading edge of article 34 c.As long as article 34 d is still being controlled by first conveyor 22,this gap will not change. However, as soon as article 34 d transitionsto being controlled by second conveyor 24, which is traveling at ahigher speed than first conveyor 22, article 34 d will begin to advanceforwardly from article 34 c, thus either creating a gap between articles34 c and d, or enlarging whatever gap may have already pre-existed. FIG.3 depicts the moment when the control point 52 of article 34 d hasreached reference point 50. At this moment, article 34 d begins toseparate from article 34 c, thus creating a gap between articles 34 cand d. This gap is illustrated in FIG. 3 and detected by an unobstructedbeam of electromagnetic energy 54 from photo-detector array 42. Bymonitoring which particular photo-detector in array 42 detects thisnewly created or expanded gap, the control point of article 34 d can bedetermined by a calculator 56. Because the distance that each individualphoto-detector is positioned away from reference point 50 is known,calculator 56 can simply calculate the control point 52 as being thissame distance. This calculation of the location of control point 52,however, is based upon the longitudinal distance of control point 52from the trailing edge of article 34 d. Typically, it will be desirableto know the location of control point 52 with respect to a differentlandmark such as, for example, the leading edge of article 34 d.Calculator 56 can easily compute this location of control point 52 bysubtracting the longitudinal distance of control point 52 to thetrailing edge of article 34 d from the overall length of article 34 d.Alternative calculation methods are, of course, also possible.

[0027] The length of article 34 d can be determined in a variety ofdifferent manners. One way is to have photo-detector array 42 monitorthe leading edge of article 34 d while it is within the detection zoneof array 42. Once out of this detection zone, the speed of firstconveyor 22 is recorded until the change in the gap between articles 34d and 34 c occurs. At the moment at which this change in gap occurs, therecorded speed of conveyor 22 can be used to determine the distancearticle 34 d has traveled between the time its leading edge left thephoto-detector detection zone and the speed change occurred. Thisdistance will be equal to the distance of control point 52 from theleading edge of article 34 d.

[0028] The determination of the location of control point 52 isdependent upon what reference point is used to define control point 52.As discussed above, reference point 50 was used to define the locationof control point 52. Other reference points could be used. For example,reference point 58 could alternatively be used to define control point52. Reference point 58 is located at the very edge of the downstream endof first conveyor 22. If reference point 58 is used as the referencepoint, the control point 52 will be the location on article 34 that isaligned with reference point 58 at the moment the control of article 34transitions from that of first conveyor 22 to that of second conveyor24. This control point will correspond to a different physical locationon article 34 due to the different locations of reference points 50 and58. Reference point 60, which is located at the very edge of theupstream end of conveyor 24, could also be used as a reference point.And, as noted, any other reference point can be used in defining thecontrol point so long as the particular reference point is known andused consistently throughout the rest of the conveyor system.

[0029] The determination of control point 52 as described hereininvolves, in one embodiment, the creation or enlargement of gaps betweenarticles as they transition from conveyor 22 to conveyor 24, and thecreation or enlargement of these gaps may be desirably controlled. Thesegaps are created or enlarged as a result of the higher speed of secondconveyor 24 with respect to first conveyor 22. If conveyor 22 is set torun at a fixed fraction of the speed of conveyor 24, then the gaps thatare created between articles transitioning from conveyor 22 to conveyor24 will vary as the length of the articles vary. For example, if onlylong articles are moved over conveyor 22, they will tend to haverelatively large gaps. If only small articles are moved, they will tendto have relatively smaller gaps. If both small and large articles areconveyed by conveyors 22 and 24, they will tend to have gaps of varyinglength. The varying lengths are due to the different amounts of timelong and short articles spend moving at the speed of first conveyor 22while the immediately downstream article is moving at the higher speedof second conveyor 24. This disparity in gap lengths is often desirablyreduced or eliminated.

[0030] The reduction in the disparity of gap lengths between articlesexiting control point determination module 38 may be desirable forseveral reasons. First, any downstream gap controlling system, such asgap control system 40, may not operate as effectively when articles arebeing input into the system with widely varying gaps. This may be becomemore of a problem as conveyor speeds increase. Second, if the gapscreated in control point determination module 38 were larger than thedesired gaps, they would have to be eliminated downstream by the gapcontrol system. Having to eliminate gaps created by control pointdetermination module 38, of course, makes the gap control system have towork harder, and therefore makes the system less efficient.

[0031] In order to carry out this reduction in gap variation, acontroller could be added that controls the speed of first conveyor 22such that, as soon as control point 52 is measured, the speed of firstconveyor 22 is immediately brought up to that of second conveyor 24.This will substantially prevent the gaps from getting any larger afterthe control point is determined, and will tend to reduce the disparityin gaps that would otherwise result for large and small articles if theconveyor speeds remained at a fixed ratio. After the speed of conveyor22 has been brought up to that of conveyor 24, the existing gaps willnot change. The controller would maintain conveyor 22 at the same speedas conveyor 24 up until the moment the control point reached thereference point. At that moment, the controller would decrease the speedof conveyor 22 with respect to conveyor 24 down to an acceptably lowerspeed such that the control point of the next article could be measured.After this was measured, the speed of conveyor 22 would then beincreased to that of conveyor 24 again, and so on. Alternatively, itwould be possible to implement this controller by having it makeadjustments to the speed of second conveyor 24, rather than firstconveyor 22.

[0032] After calculator 56 has determined the control point of anarticle, this information can be fed to whatever other systems, modules,or structures that can make use of this information. In the embodimentdepicted in FIG. 1, this information is fed to gap control system 40where it is used to more accurately control the gapping of articlesexiting on takeaway conveyor. Alternatively, this information could beused in an induct process such as that described in commonly assigned,U.S. patent application Ser. No. 09/699,170, filed Sep. 25, 2000, andentitled High Rate Induction System, the disclosure of which is herebyincorporated herein by reference.

[0033] Gap control system 40 includes a horizontal array ofphoto-detectors 62 which may be of the same type of photo-detectors asarray 42. Array 62 is located alongside a portion of conveyor 24, aportion of conveyor 32, and the gap between conveyor 24 and conveyor 32.Array 62 preferably, although not necessarily, extends for a distanceequal to the maximum expected length of articles that will be conveyed.A gap detector 64 receives the output from array 62 and uses it todetermine the gap or gaps between articles that are traveling within thezone of detection of array 62. As illustrated in FIG. 1, gap detector 64would detect both the gap between articles 34 e and f and the gapbetween articles 34 f and g. Gap detector 64 detects these gaps bydetermining which individual photo-detectors are obstructed by articles,and which are not. Based either upon the number of photo-detectors thatare not obstructed between articles, or the distance between the mostwidely separated, non-obstructed set of continuous photo-detectors, thelength of a gap can be determined. Also, by determining which individualphoto-detectors are not obstructed, the location of the gap with respectto conveyor 24 can be determined based upon the known position of eachof the photo-detectors.

[0034] After gap detector 64 detects the one or more gaps which arewithin the detection zone of array 62, it passes this information to agap selector 66. Gap selector 66 chooses which of the gaps detected bydetector 64, if there are more than one, to use in the feedback controlloop that controls the speed of conveyor 24. The decision of which gapto use is based upon the location of the control point 52. In theposition illustrated in FIG. 1, the control point 52 of article 34 f hasnot yet reached the center of the space between conveyors 24 and 32. Thespeed of article 34 f is therefore still being controlled by conveyor24. By adjusting the speed of conveyor 24, it is therefore stillpossible to adjust the gap between article 34 f and article 34 g. Gapselector 66 would therefore choose this gap (between articles 34 f andg) as the gap to be used within the feedback control loop. Thedimensions of this gap would then be fed into a comparator which alsoreceives an input from a desired gap 70. The desired gap 70 can bechosen according to the needs of the rest of the conveying system, orcan be chosen in any other manner. As illustrated in FIG. 1, the gapbetween articles 34 g and 34 h should correspond to the desired gap.Comparator 68 compares the measured gap from gap selector 66 to thedesired gap 70 and outputs the difference between these gaps to afeedback controller 72. Feedback controller 72 outputs a command to avariable speed motor controller 74 that causes controller 74 to changethe speed of conveyor 24 as commanded. This command is generated inresponse to the difference between the measured gap and the desired gap70. Variable speed motor controller 74 outputs a signal to a motor 76that powers conveyor 24. The particular type of motor 76 is not limitedby the present invention and the location of motor 76 with respect toconveyor 24 can vary from that depicted in FIG. 1.

[0035] Feedback controller 72 may be any type of feedback controller,such as a proportional-integral-derivative (PID) controller, or anyother type of feedback controller. The particular form of the feedbackequation or equations used by feedback controller 72, along with theparticular constants or gains used in the equation(s), will varydepending upon the type of controller used, the responsiveness of thecontrolled motor or motors, the feedback rate, and other factors, aswould be understood by one skilled in the art. While other command ratescan be used, having feedback controller 72 update and issue commandsapproximately twenty times per second should generally be sufficient.The commands issued from feedback controller 72 may be either digital oranalog. If digital, the operating range of the motor is preferablydigitized such that it can be commanded to operate at over one hundreddifferent speeds. Less digitization, however, can also be used withinthe scope of the invention. The repetitive measuring of the article gapsby array 62 may take place at the same rate as the commands are issuedfrom controller 72, or a different rate.

[0036] As article 34 f moves along conveyor 24, feedback controller 72will repeatedly issue commands to motor 76 to adjust its speed in orderto create the desired gap between articles 34 f and 34 g. Feedbackcontroller 72 will continue to output commands to adjust the gap betweenarticle 34 f and article 34 g until control point 52 reaches themidpoint between conveyors 24 and 32 (assuming the control point to bebased on a reference point midway between conveyors). When control point52 has reached this midpoint, article 34 f is no longer being controlledby conveyor 24, despite the portion of article 34 f that is stillphysically located on conveyor 24. Adjustments to motor 76 in order tochange the gap between articles 34 f and 34 g are therefore ineffective.Thus, when control point 52 of article 34 f has reached the midpointbetween conveyors 24 and 32, gap selector 66 chooses the gap betweenarticles 34 e and f as the gap whose dimensions are being input intocomparator 68. Thereafter, any adjustments in the speed of motor 76 willaffect the gap between articles 34 e and f, rather than articles 34 fand g. Any necessary adjustments to the gap between articles 34 e and fwill continue to be implemented by gap control system 40 until thecontrol point of article 34 e reaches the midpoint between conveyors 24and 32. At that point, the gapping control will switch to the nextdownstream gap, and so on.

[0037] By being able to accurately determine the control point of eacharticle, such as by using control point determination module 38, thecontrol of the gapping performed by gap control system 40 is enhanced.Such control point information allows the gap control system 40 tocontinue to make any necessary changes in the gap of interest right upuntil such control is no longer possible. Such control point informationalso helps ensure that the changes being made to the speed of conveyor76 will affect only the intended gap and not others. As statedpreviously, the invention contemplates that such control pointinformation may come from control point determination module 38, or itmay come from other sources as well. For example, it would be possibleto utilize gap control system 40 wherein the control point informationwas merely an assumption as to the location of the control point, suchas the center point of the article. While such a system would likely bemore inaccurate than a system in which the control point was actuallymeasured, gap control system 40 finds equal applicability to such asystem.

[0038] It will be understood by one skilled in the art that theparticular conveyor arrangement indicated in FIG. 1 could varysignificantly from that depicted. For example, it would alternatively bepossible to implement gap control system 40 in a manner in which theconveyor whose speed was modified to control the gaps was the downstreamconveyor, rather than the upstream conveyor. It would also be possibleto implement multiple gap control systems 40 sequentially. Such asequential array of gap control systems might further increase theaccuracy of the final gap, particularly where the desired gap differssubstantially from the gaps that pre-exist between the articles beingfed into gap control system 40. In still another alternative, gapcontrol system 40 could be modified to include one or more additionalconveyors upstream of conveyor 24 that used an open loop type of controlin order to make refinements to the article gaps such that gappingcontrol system 40 only had to make minor adjustments, if any, to createthe desired gaps. In still another alternative embodiment, thehorizontal photo-detector arrays could be replaced by other sensors thatprovided repeated updates about the status of gaps and the position ofarticles. One such sensor could be a camera or cameras appropriatelymounted to visually record the movement of articles. Such video imagescould be processed by the appropriate software in order to measure thegaps and article lengths in order to provide input into the feedbackloop. An acoustic sensor could also be used as an alternative to thephoto-detector array, as well as still further types of sensors.

[0039] As still another variation, it would possible to adapt feedbackcontroller 72 to limit the acceleration that motor 76 is commanded toundertake. Such limits on acceleration would primarily be designed toavoid tipping any of the articles traveling on conveyor 22. Such limitscould be modified based on the determination of control point 52. Themore forwardly control point 52 is located on the article to beaccelerated, the more acceleration the article can generally withstandwithout tipping, when all other factors remain equal. If provisions aremade to determine the height of the article, this information can alsobe used to determine the appropriate acceleration that an article canundergo without tipping. The length of the article could also befactored into the determination of the acceptable acceleration for anarticle, as would be understood by one skilled in the art.

[0040] While the present invention has been described in terms of thepreferred embodiments depicted in the drawings and discussed in theabove specification, along with several alternative embodiments, it willbe understood by one skilled in the art that the present invention isnot limited to these particular embodiments, but includes any and allsuch modifications that are within the spirit and the scope of thepresent invention as defined in the appended claims.

What is claimed is:
 1. A method for determining a control point of anarticle traveling on a conveyor system comprising: providing a firstconveyor having a downstream end, said first conveyor having a firstarticle conveying surface; providing a second conveyor having anupstream end aligned with said downstream end of said first conveyor,said second conveyor having a second article conveying surface operatingat least occasionally at a different speed than said first articleconveying surface; and detecting when a change occurs in the speed of anarticle due to said article having moved sufficiently from said secondconveying surface to said first conveying surface such that the speed ofsaid article is controlled by said second conveying surface rather thansaid first conveying surface.
 2. The method of claim 1 wherein saidcontrol point is set to be the point on said article which is alignedwith a fixed reference point when said change in speed occurs.
 3. Themethod of claim 1 wherein said detecting of said change in speed of saidarticle comprises detecting a change in spacing between said article andan upstream article adjacent to said article.
 4. The method of claim 2wherein said fixed reference point is located halfway between said firstand said second conveyors.
 5. The method of claim 1 further comprising:providing a horizontal array of photo-detectors positioned alongsidesaid first conveyor; and monitoring said photo-detectors to determinewhen said change in speed of said article occurs.
 6. The method of claim5 further comprising detecting a change in spacing between said articleand an upstream article adjacent to said article.
 7. The method of claim1 further including adjusting the relative speed of said first conveyingsurface with respect to said second conveying surface after said controlpoint has been determined.
 8. The method of claim 7 wherein theadjusting of the relative speed of said first conveying surface withrespect to said second conveying surface includes setting the speeds ofsaid first and second conveying surfaces equal to each other.
 9. Themethod of claim 1 further including detecting a front edge of saidarticle, determining the position of said front edge of said article onsaid second conveying surface when said change in speed occurs, andcomputing the distance of said front edge to said control point of saidarticle.
 10. A method of controlling a gap between a first article and asecond article traveling on a conveyor system comprising: providing afirst conveyor; providing a second conveyor aligned with said firstconveyor, said second conveyor operating at a different speed than saidfirst conveyor; measuring the control point of said first article assaid first article passes from said first conveyor to said secondconveyor; measuring any gap between said first article and said secondarticle while said first article is traveling at least partially on anadjustable speed conveyor; comparing said measured gap to a desired gap;and adjusting the speed of said adjustable speed conveyor while saidsecond package is not on said adjustable speed conveyor in order toreduce any difference between said measured gap and said desired gap.11. The method of claim 10 wherein said adjustable speed conveyor is thesame as said second conveyor.
 12. The method of claim 10 wherein saidmeasuring of said gap comprises: measuring the location of a leadingedge of said first article at a particular time; measuring the locationof a trailing edge of said second article at substantially the same timeas said leading edge of said first article is measured; and determiningthe distance between said leading edge of said first article and saidtrailing edge of said second article.
 13. The method of claim 10 furthercomprising: re-measuring said gap between said first article and saidsecond article while said first article is at least partially still onsaid adjustable speed conveyor; and readjusting said speed of saidadjustable speed conveyor based upon any difference between saidre-measured gap and said desired gap.
 14. The method of claim 13 whereinsaid re-measuring of said gap and said readjusting of said speed arerepeated multiple times per second.
 15. The method of claim 10 whereinmeasuring the control point of said first article as said first articlepasses from said first conveyor to said second conveyor comprises:detecting when a change occurs in the speed of said first article due tosaid first article having reached said second conveyor; and determiningsaid control point of said first article to be the point on said firstarticle which is aligned with a fixed reference point when said changein speed occurs.
 16. The method of claim 15 wherein said detecting ofsaid change in speed of said first article comprises detecting a changein spacing between said first article and a third article adjacent toand upstream of said first article.
 17. The method of claim 10 whereinsaid first article is positioned upstream from said second article. 18.The method of claim 10 wherein said measuring of any gap between saidfirst article and said second article further comprises providing ahorizontal array of photo detectors positioned at least partially alongsaid adjustable speed conveyor.
 19. The method of claim 18 wherein saidarray of photo detectors includes an array of photo emitters positionedalong a first side of said adjustable speed conveyor and an array ofphoto receptors positioned along a second side of said adjustable speedconveyor, said array of photo emitters periodically emittingelectromagnetic signals which are detected by said array of photoreceptors unless one or more articles are positioned on said adjustablespeed conveyor between said array of photo emitters and said array ofphoto receptors.
 20. The method of claim 10 further including measuringsaid length of said first article.
 21. The method of claim 10 furtherincluding limiting the acceleration of said adjustable speed conveyor.22. The method of claim 21 further including changing the limit of theacceleration of said adjustable speed conveyor based at least partiallyupon the measurement of the control point of said first article.
 23. Amethod of controlling a gap between a first article and a second articletraveling on a conveyor system comprising: providing a first conveyor,said first conveyor being an adjustable speed conveyor; providing asecond conveyor aligned with said first conveyor; measuring any gapbetween said first article and said second article at a first moment intime while said first article is at least partially positioned on saidfirst conveyor; calculating any difference between a desired gap andsaid gap measured at a first moment in time; generating a first commandfor adjusting the speed of said first conveyor in order to reduce anydifference between said desired gap and said gap measured at a firstmoment in time, said command being based upon said difference betweensaid desired gap and said gap measured at a first moment in time;measuring any gap between said first article and said second article ata second moment in time while said first article is at least partiallypositioned on said first conveyor; calculating any difference betweensaid desired gap and said gap measured at a second moment in time; andgenerating a second command for adjusting the speed of said firstconveyor in order to reduce any difference between said desired gap andsaid gap measured at a second moment in time, said second command beingbased upon said difference between said desired gap and said gapmeasured at a second moment in time.
 24. The method of claim 23 whereinsaid measuring of any gap at either said first or said second moment intime comprises: measuring the location of a leading edge of said firstarticle at a particular time; measuring the location of a trailing edgeof said second article at substantially the same time as said leadingedge of said first article is measured; and determining the distancebetween said leading edge of said first article and said trailing edgeof said second article.
 25. The method of claim 23 wherein said firstconveyor is positioned upstream of said second conveyor.
 26. The methodof claim 25 wherein said first article is positioned upstream of saidsecond article.
 27. The method of claim 23 wherein said first command isproportional to the difference between said desired gap and said gapmeasured at a first moment in time.
 28. The method of claim 23 whereinsaid first and second commands are generated within one second or lessof each other.
 29. The method of claim 27 wherein said measuring of saidgaps at said first and said second moments in time occurs less than onesecond apart.
 30. The method of claim 23 wherein said measuring of anygap at said first moment in time further comprises providing ahorizontal array of photo detectors positioned at least partially alongsaid first adjustable speed conveyor.
 31. The method of claim 23 whereinsaid first command can specify at least one hundred different speeds forsaid first adjustable speed controller.
 32. The method of claim 23further including measuring a control point of said first article assaid first articles passes over a transition point between twoconveyors.
 33. The method of claim 32 wherein said two conveyorscomprise said first adjustable speed conveyor and a third conveyorlocated upstream of said first adjustable speed conveyor.
 34. The methodof claim 32 wherein said measuring of said control point comprises:detecting when a change occurs in the speed of said first article assaid article crosses said transition point; and determining said controlpoint of said first article to be the point on said first article whichis aligned with a fixed reference point when said change in speedoccurs.
 35. The method of claim 34 wherein said detecting of said changein speed of said first article comprises detecting a change in spacingbetween said first article and a third article adjacent to and upstreamof said first article.
 36. The method of claim 32 further includinglimiting the acceleration of said first adjustable speed conveyor basedat least partially upon the measurement of said control point.
 37. Adevice for measuring a control point of an article traveling on aconveyor system comprising: a first conveyor; a second conveyor alignedwith said first conveyor and downstream of said first conveyor, saidsecond conveyor operating at a different speed than said first conveyor;and a sensor adapted to detect when a change in speed occurs in saidarticle due to said article having moved sufficiently onto said secondconveyor such that second conveyor controls the speed of said article.38. The device of claim 34 further including a controller whichcalculates the control point of said article to be a point on saidarticle which is aligned with a fixed reference point when said changein speed occurs.
 39. The device of claim 38 wherein said reference pointis located halfway between said first and said second conveyors.
 40. Thedevice of claim 37 wherein said sensor comprises a horizontal array ofphoto-detectors positioned alongside said first conveyor.
 41. The deviceof claim 40 wherein said horizontal array of photo-detectors extends fora horizontal distance at least equal to the distance of the greatestexpected length of said article.
 42. The device of claim 41 wherein saidhorizontal array of photo-detectors has an upstream end and a downstreamend, said downstream end being placed midway between said first and saidsecond conveyors, and said upstream end being placed upstream of saiddownstream end.
 43. A conveyor induct system comprising: a firstconveyor; a second conveyor aligned with said first conveyor, saidsecond conveyor operating at a different speed than said first conveyor;a first sensor which measures the control point of said first article assaid first article passes from said first conveyor to said secondconveyor; a second sensor which measures any gap between said firstarticle and said second article while said first article is traveling atleast partially on an adjustable speed conveyor; and a controller whichcompares said measured gap to a desired gap and adjusts the speed ofsaid adjustable speed conveyor while said second package is not on saidadjustable speed conveyor in order to reduce any difference between saidmeasured gap and said desired gap.
 44. The system of claim 43 whereinsaid adjustable speed conveyor is the same as said second conveyor. 45.The system of claim 43 wherein said first sensor comprises a horizontalarray of photo-detectors.
 46. The system of claim 45 wherein said secondsensor comprises a horizontal array of photo-detectors.
 47. The systemof claim 46 wherein said second sensor measures the location of aleading edge of said first article and a trailing edge of said secondarticle at substantially the same time.
 48. The system of claim 43wherein said second sensor measures any gap between said first and saidsecond article at least ten times per second.
 49. A conveyor inductsystem comprising: a first conveyor, said first conveyor being anadjustable speed conveyor; a second conveyor, said second conveyoraligned with said first adjustable speed conveyor, said second conveyoroperating at a different speed than said first conveyor; a sensor whichrepetitively measures any gap between said first article and said secondarticle while said first article is at least partially positioned onsaid first adjustable speed conveyor; a feedback controller whichreceives information from said sensor, said feedback controllercalculating any difference between said measured gap and a desired gap,said feedback controller outputting a command for adjusting the speed ofsaid adjustable speed conveyor based upon any difference between saidmeasured gap and said desired gap.
 50. The device of claim 49 whereinsaid sensor comprises a horizontal array of photo-detectors.
 51. Thedevice of claim 50 wherein said horizontal array of photo-detectorsextends from said first to said second conveyor such that a portion ofsaid horizontal array is positioned alongside said first conveyor and aportion of said horizontal array is positioned alongside said secondconveyor.
 52. The device of claim 49 wherein said first conveyor ispositioned upstream of said second conveyor.
 53. The device of claim 52wherein said first article is positioned upstream of said secondarticle.
 54. The device of claim 49 wherein said feedback controller isa proportional-integral-derivative controller.
 55. The device of claim49 wherein said feedback controller outputs multiple commands per secondto adjust the speed of said adjustable speed conveyor.